The present invention relates to fluid spray volume control and more particularly to an automatic volume control system for controlling the rate at which a substance, such as paint, is deposited on an adjacent surface from a mobile vehicle as a function of vehicle speed.
It is necessary during the application of quick drying road marking materials, such as paint, that the material be applied at a thickness which is within fairly rigid upper and lower limits. If the line is too thick, the material will not dry in the prescribed time. If the line is too light, then the material will not hold its beads or will not be as durable as may be required. A factor which results in uneven paint thickness is intentional or unintentional variation in vehicle speed. In order to maintain the proper constant line thickness, the paint flow should be increased and decreased in direct proportion to increases and decreases in vehicle speed.
On conventional vehicle mounted line painting machines paint flow must be manually controlled by an operator as by manually backing off the pressure regulator or opening and closing a needle bypass valve. There is no means for automatically changing the volume requirement to correspond to the vehicle road speed.
A number of disadvantages result from the manual method of volume control. The operator must be constantly monitoring the vehicle speed and the level of paint flow, removing his attention from the other aspects of vehicle control. Human error is likely to result in line thicknesses which are uneven or incorrect thickness.
A method of metering the thickness of the paint in accordance with the vehicle speed which has been tried is to use gear pumps powered by the vehicle power take-off. The power take-off increases and decreases with the road speed of the vehicle in a specific gear, so that as the pumps go faster or slower they would meter the thickness of the paint, at least to an approximation, to correspond to the vehicle speed. However, this method has a serious disadvantage in that the mechanical drives on the gear pumps interfere with the operation of the vehicle.
The present invention overcomes the disadvantages of the prior art by providing an electronic servo system, a tachometer generator driven from one of the road wheels, which applies a voltage which is proportional to the road speed to a hydraulic valve. The hydraulic valve permits hydraulic oil to pass at a rate proportional to the applied voltage and thus to the vehicle speed.
A hydraulic pump driven by the vehicle's power take-off pumps the hydraulic oil through the hydraulic valve. The hydraulic oil in turn powers a hydraulic motor that drives a paint pump which forces paint through one or both of a pair of spray guns. The paint pump should have fairly linear characteristics so that the volume of paint pumped is proportional to the speed of the hydraulic motor and thus the road speed of the vehicle. A dual orifice bypass valve is connected across the spray guns. An intermittent line mechanism also responsive to the speed of the vehicle, is capable of intermittently, synchronously opening and closing one or both valve orifices as it turns off and on one or both of the two spray guns. The intermittent line mechanism is electrically powered by the same road wheel that drives the tachometer generator and, as is well known, is responsive to wheel speed to provide single or double intermittent lines of paint of constant length at any road speed.
In one embodiment of the invention, two separate and parallel painting systems are provided so that two colors or types of paint may be used simultaneously, e.g., yellow paint and white paint. In accordance with this embodiment, hydraulic fluid from the hydraulic pump is divided by a flow divider valve and directed to separate hydraulic valves each of which is controlled by a voltage from the tachometer generator. Separate hydraulic motors, paint pumps and spray guns are used, connected to the adjustable hydraulic divider valves as described above.
As a result of this invention, a paint truck operator need not be concerned with the film thickness of the paint lines and a constant thickness independent of vehicle speed is obtained.